Intelligent belt drive system and method

ABSTRACT

In one aspect, the invention relates to a tensioner that is capable of precognitively anticipating when it is desirable to increase the tension in a belt or other endless drive element so as to prevent belt slip prior to events that would raise the risk of it.

FIELD OF THE INVENTION

The present invention relates to tensioners for tensioning engine drivenelements such as timing belts, timing chains and accessory drive belts.In particular, the present invention is directed to belt tensioners thathave the capability to adjust the belt tension in the belt.

BACKGROUND OF THE INVENTION

Tensioners for timing belts, timing chains and accessory drive belts arewell known. Some tensioners are adjustable in terms of the amount oftension is generated in the belt during operation of the engine. Suchtensioners react to certain sensed conditions that indicate a potentialfor, or occurrence of, belt slip. While such systems may reduce thefrequency of belt slip, they are, by design, inherently permitting somebelt slip to occur. In those systems that sense the actual occurrence ofbelt slip, belt slip has already necessarily occurred before thetensioner will increase belt tension. In systems where the conditionsfor belt slip are sensed, the conditions that create the potential forbelt slip must already occur for them to be sensed by the tensioner,which inherently means therefore that belt slip can occur before thetensioner has reacted to increase belt tension.

While these systems have some advantage in terms of reducing thefrequency of belt slip, they still permit some belt slip to occur, whichmay be detrimental to the belt, to certain accessories driven by thebelt, and to the perception of quality of a person hearing the chirpthat can accompany belt slip.

Furthermore, the tension adjustment mechanisms employed by suchtensioning systems may be expensive, and/or unreliable.

It would be beneficial to provide a tensioning system that has at leastpartially addresses one or more of these problems.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to a tensioner that is capable ofprecognitively anticipating when it is desirable to increase the tensionin a belt or other endless drive element so as to prevent belt slipprior to events that would raise the risk of it.

In another aspect, the invention relates to controlling a tensioner thathas adjustable tension, in such a way as to avoid the tendency of thetensioner to cycle between high and low tension settings.

In another aspect, the invention relates to the use of one or more ofthe parameters described herein for the purpose of preventing belt slip.

In another aspect the invention relates to the embodiments of tensionersshown and described herein.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made to FIG. 1 a, which shows a crankshaft 10 from anengine 13 from a vehicle. The crankshaft 10 has a crankshaft pulley 12thereon. The crankshaft pulley 12 drives one or more vehicle accessoriesvia a belt 14. The accessories may include an alternator 16, an airconditioning compressor 18, a water pump (not shown), a power steeringpump (not shown) and/or any other suitable accessory. Each of the drivenaccessories has a shaft, and a pulley that is connectable anddisconnectable from the shaft via a clutch. The alternator shaft, clutchand pulley are shown at 50, 52 and 54 respectively. The air conditioningcompressor shaft, clutch and pulley are shown at 56, 58 and 60respectively. This permits each of the accessories to be shut off whennot needed even though the belt 14 itself is still being driven by thecrankshaft 10.

Providing at least a certain amount of tension in the belt 14 isbeneficial in that it reduces the amount of slip that can occur betweenthe belt 14 and the driven accessories or even between the belt and thecrankshaft 10. However, providing an unnecessarily high tension in thebelt 14 has many detrimental effects. For example, it causes more powerfrom the engine 13 to be consumed in driving the accessories, leavingless power for use in driving the vehicle. Thus, to achieve a particularlevel of performance from the vehicle, a greater amount of fuel would beconsumed than would be consumed if the power loss were smaller.Additionally, a high belt tension generates greater hub loads on thepulleys for the driven accessories, which necessitates the use ofrelatively larger shafts on the accessories, larger bearings to supportthe shafts, heavier brackets to hold the accessories in place, all ofwhich add to the weight of the vehicle and thereby negatively impactfuel economy for the vehicle.

A belt tensioner 20 is shown which keeps the belt 14 tensioned so as toreduce belt slip, and to keep the belt on the pulleys of the crankshaft10 and accessories. The tensioner 20 includes a tensioner pulley 22which engages the belt 14, a tensioner arm 24 which holds the tensionerpulley 22, a tensioner biasing member 26 for biasing the tensioner arm24 towards a free arm stop position (the position the arm 24 would reachif it was not pressing into the belt 14), which would represent theposition of reduced stored mechanical potential energy within theelastomeric biasing spring within the tensioner travel range, and a loadstop position (the position the arm 24 would reach if the arm 24 werepushed all the way throughout its range of travel away from the free armstop position), which would represent the position of increased storedmechanical potential energy within the elastomeric biasing spring withinthe tensioner travel range. The tensioner 20 further includes atensioner actuator 28 which is operatively connected to the tensionerpulley 22 and tensioner arm 24 to move the pulley 22 and arm 24 betweenthe free arm stop and load stop positions. The tensioner 20 may includestructure that dampens its motion.

The belt tensioner 20 may have any suitable structure that provides theaforementioned capabilities. For example, the arm 24 may telescopelinearly and may be biased outwards by a compression spring, which maybe the tensioner biasing member 26. The first end of the spring 26engages the arm 24, and a second end of the spring 24 engages a base 30.The base 30 is movable along the arm 24 by the tensioner actuator 28.For example, the tensioner actuator 28 may include an electric motorthat turns a lead screw (not shown), whose rotation drives a traveler(also not shown) forwards or backwards. The base 30 is connected to thetraveler and moves therewith. The lead screw may be hollow and the arm24 may telescope outwards from it. Thus, the arm 24 is movableindependently from the base 30 and from the lead screw. The tensioneractuator 28 is controllable to drive the base 30 forwards or backwards.Driving the base 30 forwards increases the amount of compression in thespring 26 thereby increasing the biasing force exerted by the spring 26on the arm 24 and in turn on the pulley 22 in the free arm stopdirection, thereby increasing the tensioning force exerted by theypulley on the belt 14. Driving the base 30 backwards decreases theamount of compression in the spring 26, thereby reducing the tensioningforce exerted by the pulley 22 in the free arm stop direction on thebelt 14. The biasing force of the spring 26 may be referred to as anactuator force since the actuator 28 controls the magnitude of thisforce. The tensioner actuator 28 may have any suitable motive means withwhich to drive the movement of the base 30 instead of an electric motor,such as, for example, pneumatic or hydraulic pressure, a shape memorymetal actuator, or some other means.

In an alternative embodiment shown in FIG. 1 b, the tensioner arm 24 ispivotable about a tensioner arm pivot axis. The tensioner biasing membermay be a torsion spring which is engaged at a first end with the arm tobias the arm towards the free arm stop. The second end of the torsionspring may be engaged with the tensioner actuator 28 which moves thesecond end of the spring to increase or decrease the biasing force ofthe spring on the tensioner arm 24 and therefore the tensioning force ofthe pulley 22 on the belt 14.

Examples of suitable tensioner structures may be found in PCTpublication number, WO2010/094127A1, and in U.S. Provisional patentapplications 61/382,892, 61/381,929, and 61/391,266, all of which arehereby incorporated by reference. Examples of suitable actuators thatcan be used to drive the second end of the torsion spring may be foundin U.S. Pat. Nos. 3,954,016, 4,131,306, 4,674,781, 4,850,466, 4,885,954,4,893,704, 5,338,076, 5,634,676, 5,862,903 and 5,983,739, all of whichare hereby incorporated by reference.

In reference to the tensioner embodiment shown in FIG. 1 b, the graphshown in FIG. 1 c illustrates the relationship between the length of thebelt 14, the force applied by the spring 26 on the tensioner arm 24(shown at 90), and the resulting torque applied by the tensioner arm 24on the belt 14 (shown at 92). The nominal belt length is shown at 96,and with plus and minus tolerances at 98 a and 98 b. In generalthroughout this disclosure, when it is stated that the tensioner arm isdriven into the belt 14, is engaged with the belt 14, applies torque tothe belt 14 or the like, it will be understood that it is actuallyacting on the belt 14 through the pulley. As the belt stretches, the arm24 rotates progressively further as a result of the spring force actingon it. However, the spring force progressively decreases as the arm 24rotates during belt stretch, since the spring 26 is progressivelyunwinding towards its rest position. Also, the rotation of the arm 24changes the geometric (i.e. angular) relationship of the arm 24 to theapplied hubload of the pulley 22 on the belt 14. As a result, eventhough the spring force may be decreasing linearly with rotation of thearm 24, the torque applied to the belt 14 varies non-linearly(sinusoidally in a typical configuration) with rotation of the arm 24.The result of these changes is shown in the graph in FIG. 1 d, whichillustrates the relationship between the belt tension generated by thetensioner, as a function of belt length. In theory it would beadvantageous to be able to apply a certain target tension to the beltthrough the tensioner, which was constant regardless of belt length, andhence regardless of the angular position of the tensioner arm 24. Thistarget tension is shown at 100 in FIG. 1 d. However, when using atorsion spring such as spring 26, and a rotating tensioner arm 24, thecurve shown at 102 is what results. A line indicating the nominal lengthof the belt 14 is shown at 96. The tensioner 20 is configured so thatits response curve 102 to changes in belt length, even thoughnon-linear, somewhat match up closely with the ‘target’ tension line100.

In a typical tensioner of the prior art, the response curve applied bythe tensioner is somewhat fixed in the sense that the tension applied bythe tensioner on the belt 14 changes based on belt length only (ignoringdynamic issues relating to belt flutter and the like, which cantemporarily affect the response of the tensioner). As a result, suchtensioners are typically configured to apply a relatively high targettension to the belt because they must ensure that the belt hassufficient tension in it in the worst case scenarios (e.g. under harshoperating conditions where the belt is wet, where the load on the beltis high due to operation of all of the accessories driven by the belt,due to high rates of change of the engine rpm, and the like). However,in reality these worst-case scenarios are not the norm, and under mostoperating conditions, the belt tension that is applied by these priorart tensioners is needlessly high. This constant state of high tensionin the belt unfortunately results in a needless consumption of power,overdesign of bearings and the like for pulleys that are engaged withthe belt, potentially shortened operating life of the belt, increasedemissions from the vehicle, and other disadvantages.

The tensioner 20 is capable, however, of adjusting the tension in thebelt 14 so that when the need arises for high tension, the tensioner 20is capable of increasing the tensioning force applied to the belt 14,thereby increasing the tension in the belt 14. This can result, in someembodiments in a shift upwards of the tension response curve shown inFIG. 1 d, from the curve 102, to the dashed line curve shown at 106. Thecurve 106 need not match the shape of the curve 102. Moreover theeffective spring constant applicable to the tensioner 20 when in a ‘hightension’ mode as represented by the curve 106 is not critical. Thus, theshape of the curve 106 is not particularly critical. It is importantmainly that the tension applied to the belt 14 is sufficiently high toprevent belt slip under the particular conditions that triggered thetensioner 20 to raise the tension, while ensuring that the tensionapplied to the belt 14 is not so high as to damage the belt 14 or thecomponents engaged with the belt 14 (e.g. the pulleys driving and drivenby the belt 14).

A primary purpose of providing sufficient tension in the belt 14 is toprevent belt slip, which is a condition in which the linear speed of thebelt on a pulley is different than the linear speed of the periphery ofthe pulley itself (that is where the slipping occurs). This slipping isproblematic for many reasons. One reason is that the slipping isinefficient, in the sense that the movement of the belt is not resultingin as much rotation as would be desired of the accessory driven by thepulley. Another reason is that the slipping can be audible in somecircumstances, which can result in the impression on the part of thevehicle owner or passersby that there is a quality issue with thevehicle.

It is beneficial for the tensioner 20 to be able to determine if beltslip is taking place. To do this, the tensioner 20 may determine thelinear speed of the belt 14, and the linear speed of one or more of thepulleys from accessories that are driven by the belt 14. The linearspeed of the belt 14 may be determined by determining the linear speedof a pulley that is driven by the belt, but that relatively littlerotational inertia or more broadly, resistance to rotation, associatedwith it. An example of such a pulley is the pulley 22 on the tensioner20. Such a pulley typically has no belt slip associated with it andtherefore provides a relatively accurate value for the speed of the belt14 during operation of the belt tensioning system. To provide a valuefor the speed of rotation of the pulley 22 any suitable means may beused. For example, a sensor trigger, such as a magnet or a metal target,shown at 70, may be placed in the pulley as shown in FIG. 2 a, and asuitable sensor 72, such as a Hall effect sensor may be positioned inthe tensioner arm 24. A plurality of the magnets or metal targets 70 maybe spaced equally from each other about a circle at some radius on thepulley 22. Alternatively, as shown in FIG. 2 b, a plurality of sensortriggers, such as teeth, protrusions, or conversely, recesses, could beincorporated into the pulley 22 and a suitable sensor 72, such as a Halleffect sensor, could be mounted to a stationary element, such as a basemounting to sense the passage of the sensor triggers 70.

The pulley 22 may be machined from a suitable metal, or spun from metalsheet into a flanged configuration as shown. One or more teeth,recesses, protrusions, targets or other sensor triggers 70 may bemachined into whichever edge of the pulley passes overtop of the sensor72. As an example, the pulley may be machined from magnetic steel.

The sensor 72 is positioned to be able to detect the passing of thesensor triggers. For balance purposes, should the pulley be required tospin at very high RPM, it may be beneficial to have at least two sensortriggers 70 that are equally spaced apart on the pulley flange so as tobalance the inertia of the targets when the pulley 22 spins at highspeed.

As more sensor targets 70 are provided at equal spacings on the pulleyedge the balance of the pulley 22 improves. Thus for applications wherethe pulley's RPM is high, it is more beneficial to configure the pulley22 with an increased number of sensor triggers 70 to improve its dynamicbalance. As the number of teeth (or more generally, sensor triggers 70)increases, the accuracy of the determined RPM increases in addition tothe improvement in balance. As shown in FIG. 2 b the pulley 22 may haveany suitable number of sensor triggers 70, such as, 10 sensor triggers.

The sensor 72 may include a processor which counts the passage thesensor triggers 70 overhead, and thereby determine the instantaneous RPMof the pulley 22. Once the RPM of the pulley 22 is known, the belt speedcan be determined with high accuracy.

The pulley 22 may be used for determining the belt speed as describedabove, provided that there is sufficient belt wrap on the pulley 22.Additionally, in some circumstances there may not be sufficient room toinstall the sensor 72 or the triggers 70 on the tensioner arm 24 orpulley 22. If any of these conditions exist such that the belt speedcannot be determined using the tensioner 20, a separate idler pulley canbe installed in a separate location in engagement with the belt 14wherein a sufficient amount of belt wrap is provided.

An engine controller shown at 32 is provided in the vehicle and controlsthe operation of the engine 13 and the accessories. The enginecontroller 32 may be referred to as the vehicle control unit 32. Thevehicle control unit 32 may receive sensor data from several sources,including signals from a speed sensor on the crankshaft 10 thatindicates the speed of rotation of the crankshaft 10. The belttensioning system, which includes the tensioner 20, may further includea tensioning system controller shown at 34. The tensioning systemcontroller 34 controls the operation of the tensioner actuator 28. Thetensioning system controller 34 additionally may receive signals fromone or more other components indicative of the states of thosecomponents. For example, the tensioning system controller 34 may receivesignals indicative of the crankshaft speed, the alternator voltageoutput, the alternator speed, the alternator temperature, the positionof the tensioner biasing member 24, and the speed of the tensionerpulley 22 (as described above, using one or more sensor triggers 70 andsensor 72). The controller 34 can determine if any slip is occurring atany of the pulleys for the crankshaft 10, the alternator 16 and thecompressor 18 based on any detected differences between their actualmeasured speed and the speed they should be rotating at based on theirpulley diameter as compared to that of the tensioner pulley 22. If anyslip is detected, or if the slip detected on any pulley exceeds an upperthreshold value, such as about 3% to about 4%, the controller 34 mayincrease the actuator force so as to increase belt tension, so as toreduce or completely eliminate the slip. The increase in the actuatorforce may be by a discrete amount such as 25N after which the slip isrechecked to determine if it is below the upper threshold value.Alternatively, the increase in the actuator force may be continuous withcontinuous determination of the slip being made by the controller 34. Ineither case the controller 34 may stop increasing the tension once itdetermines that the slip is below the threshold value for all pulleys.Conversely, if the slip detected on all the pulleys is below a lowerthreshold value (which may be, for example, about 2%), then thecontroller may decrease the actuator force so as to reduce belt tensionin order to provide improved fuel economy and reduce power losses. Thedecrease may be continuous, or it may be in discrete amounts.

The tensioning system controller 34 may also receive signals from thevehicle control unit 32 indicating what action the vehicle control unit32 is about to take. For example, the vehicle control unit 32 mayindicate to the tensioning system controller 34 that it is about to turnon the air conditioning compressor 18. As a result, the tensioningsystem controller 34 may be capable of using the incoming signals todetermine that belt slip is about to occur, or that the load on the belt14 is about to increase. In case of one of these determinations thetensioning system controller 34 may pre-emptively increase the actuatorforce on the tensioner pulley 22 so as to increase the belt tensionprior to these events occurring. As a result, the belt slip is reduced(or even prevented).

In another scenario, where the vehicle is off, as the driver of thevehicle approaches the vehicle, the tensioning system controller 34 maysense the presence of the key fob, similar to the systems that sense thepresence of the key fob for the purpose of unlocking the vehicle's doorsin some luxury cars today. Instead of the controller 34 directly sensingthe presence of the key fob, the vehicle may communicate to thecontroller 34 that some other system (such as the system responsible forunlocking the vehicle doors when sensing the presence of the key fob invehicle so equipped). Alternatively, the tensioning system controller 34may detect that the key fob was used to unlock the driver's door (by auser pressing an ‘unlock’ button on the key fob). As a result, thetensioning system controller 34 may determine that the vehicle's engine13 may be started imminently. Engine startup introduces a relativelyhigh load on the belt 14, and can cause belt slip in a belt that isunder too little tension. In order to reduce the likelihood of beltslip, the tensioning system controller 34 may increase the actuatorforce on the tensioner pulley 22 prior to engine startup so as toprevent belt slip from occurring.

Instead of sensing the key fob, a less expensive option may be for thecontroller 34 to be programmed to increase the belt tension at certaintimes of the day on certain days. For example, the controller 34 may beequipped with a clock or may be programmed to determine the time anddate from some other subsystem in the vehicle such as a GPS receiver,and may be programmed to detect patterns in terms of the times of daythat the vehicle is driven. For example, the controller 34 may determinethat, over the previous 30 days (or over any other suitable number ofdays) the vehicle has been started up on weekdays (i.e. Monday toFriday) at between 7:45 am and 7:55 am over 90% of the time and neverearlier than 7:37 am. The controller 34 may be further programmed to usethis data to determine a time of day to increase the belt tension inanticipation that the engine will shortly be started. For example, thecontroller 34 may increase the belt tension at 7:43 am every weekday,or, for example, at 7:35 am every weekday. After increasing the tensionin the belt 14, the controller 34 may enter, or return to, a sleep modeuntil it is awakened by some input, such as by the detection of thevehicle being started. In addition, time of day and date information canbe used to predict the need for high tension in the belt 14 in otherways. For example, in embodiments where a humidity sensor or a moisturesensor are not present, the controller 34 may determine that, based onthe time of day (e.g. early morning) and the date (e.g. early fall),there is an increased likelihood of belt slippage from dew on the belt14. As a result, the controller 34 may be programmed to keep the belt 14under high tension for a selected period of time after engine start upto allow the engine to warm up and the dew to evaporate. Conversely, inthe mid-afternoon on a summer day, the controller 34 may be programmedto keep the belt 14 under high tension for a shorter selected period oftime after engine start up due to an expectation that there is no dew onthe belt 14.

Another example is where the controller 34 receives data from an ABSsystem and/or a traction control system to determine whether there isrepeated pending wheel lockup or pending wheel slip during a particularuse of the vehicle. This data, optionally in combination withtemperature data and/or time and date data, can be used to infer thatthere is snow on the ground, or, depending on the sensed temperature, toinfer that there may be slush or water on the ground. If snow, slush orwater is inferred to be on the ground, then the controller 34 maydetermine that the belt tension should be increased due to the potentialfor the belt 14 to become wet from kickup or some other reason duringdriving, for example. If the temperature is below a selected level, thecontroller 34 may determine that the belt 14 is likely to be relativelystiff, and possibly loose. Also, at low temperature, grease or otherlubricants used to facilitate the rotation of bearings and the liketends to ‘stiffen’ thereby increasing the resistance to turning of anyrotating components. As a result, below a certain temperature, thecontroller 34 may therefore increase belt tension.

In another example, the tensioning system controller 34 may receive asignal that the humidity is high from a sensor such as a humiditysensor. This can be an indication that it is raining, or that thevehicle is in some sort of situation where the belt 14 is potentiallywet. When the belt 14 is wet, it will be understood that there is anincreased likelihood of belt slip at any given belt tension, as comparedto a dry belt 14. When the tensioning system controller 34 determinesthat the humidity is high, the tensioning system controller 34 mayautomatically increase the actuator force on the pulley 34 so as toreduce the potential for belt slip. In a scenario where the tensioningsystem controller 34 has determined that a particular level belt tensionis suitable for a particular situation, the tensioning system controller34 may augment the belt tension to a higher level in a situation whereit detects high humidity. An example of a suitable humidity sensor is anHIH series humidity sensor provided by Honeywell International Inc.Instead of, or in addition to, a humidity sensor, the belt tensioningsystem may include some other sensing means to detect a wet belt 14 orthe potential for a wet belt 14, to trigger it to increase the belttension. For example, a temperature sensor positioned to detect thetemperature in the engine bay may be used, in conjunction with anambient temperature sensor and a humidity sensor, to detect thepotential for a wet belt in certain situations. A humidity sensor thatis configured to determine relative humidity in the engine bay, wouldinclude a temperature sensor that would be positioned to detect thetemperature in the engine bay. For example, when a vehicle is kept in acool location such as in a garage or an underground parking lot, and isthen started up and taken out on a hot day, there is the potential forwater vapour in the air to condense on many components of the relativelycool vehicle including the accessory drive belt and the pulleys itengages, which can lead to belt slip or belt chirp. To handle this, thetensioning system controller 34 may be programmed to sense when thetemperature in the engine bay is lower than the ambient temperature bymore than a selected amount while the humidity is above a selectedlevel, and if so, to increase the belt tension to a selected hightension setting. After the engine bay has warmed up (e.g. by operationof the engine) the controller 34 may determine that there is no longerthe potential for belt slip or belt chirp and may accordingly reduce thebelt tension.

In order to determine whether it is raining, the controller 34 mayreceive signals from both the humidity sensor, and from the windshieldwiper system. If the humidity is high and the windshield wipers are on,then the controller 34 may determine that it is raining. If the humidityis high but the windshield wipers are off, then the controller 34 maydetermine that it is not raining. If the humidity is not high but thewindshield wipers are on, the controller may determine that it is notraining. As an example, the windshield wipers may have been put on forsome other reason, such as to clean the windshield of dirt, snow orfrost for example.

In yet another example, the tensioning system controller 34 may receivesignals from the throttle sensor or from the vehicle control unit 32that the driver is driving aggressively, and is repeatedly acceleratingrapidly and/or is repeatedly letting off the throttle rapidly. In a lesssophisticated embodiment, each time the driver accelerates (particularlyif they accelerate hard), the tensioning system controller 34 will drivethe actuator force up to increase the belt tension to prevent slip, andeach time the driver suddenly releases the throttle, the tensioningsystem controller 34 will drive the actuator force down to decrease thebelt tension since high tension may be considered not necessary. It willbe understood that driving the actuator 28 consumes energy. Repeatedlydriving the actuator force up and down can in some situations consume asmuch or more power than is saved by the overall reduction in averagebelt tension, and can shorten the life of the tensioner actuator 28 andother components. In a more sophisticated embodiment, after a sufficientnumber of repetitions of these actions, the tensioning system controller34 may determine that this driving behaviour is likely to continue andas a result, the tensioning system controller 34 may simply leave thetensioning force at a high setting, so as to prevent hunting of theactuator 28 to reduce and increase the tensioning force in an attempt toachieve a constantly moving or oscillating target. Once the tensioningsystem controller 34 detects that the driver's driving behavior haschanged and he/she is no longer driving as aggressively for a sufficientperiod of time, the tensioning system controller 34 may decide to permitthe reduction of the belt tension. There are several ways of determiningwhether the driver of the vehicle is driving aggressively. One way is toreceive signals relating to the engine rpm. If the controller 34determines that the engine rpm cycles between a level that is above afirst, ‘high’ level and a level that is below a second, ‘low’ level thenthe controller may determine that the vehicle is being drivenaggressively. A parameter that may also be used by the controller 34 forthis determination is the cycle time. In other words, if the engine rpmreaches into the ‘high’ range (i.e. above the ‘high’ level) and thenfalls into the ‘low’ range (i.e. below the ‘low’ level) sufficientlyslowly, the controller 34 may determine that the engine is not ‘cycling’and that this does not constitute sufficiently aggressive driving towarrant leaving the tensioning force in a high tension setting. However,if the engine rpm cycles between the ‘high’ range and the ‘low’ range inrelatively short periods of time, then the controller 34 may determinethat the engine is cycling and that this does constitute a situationwhere leaving the tensioner in a high tension setting is warranted. Itwill be noted that even if the controller 34 uses signals from thethrottle sensor, the controller 34 can still be said to be basing thedetermination of whether the engine is cycling on engine rpm since thesignals from the throttle sensor can have a rough correlation to enginerpm.

Another way of using the engine rpm is for the controller 34 to use therate of change of the engine rpm to determine whether or not to leavethe tensioner at a high tension setting. If the rate of change of theengine rpm repeatedly exceeds a particular ‘high’ level then thecontroller 34 may determine that the engine is cycling and may leave thetensioner at a high tension setting regardless of the actual engine rpmreached.

The controller 34 may be programmed to store events where it hasdetermined that the vehicle is being driven aggressively in a databaseand may additionally store other information related to the event, suchas, for example, the time of day, or some type of identificationinformation that identifies which driver is driving the vehicle. Forexample, upon entry into the vehicle, the driver may have pushed one ofthe seat position memory buttons. This seat position button identifiesthe driver of the vehicle as Driver #2. The controller 34 may store thedriver identification in memory. In the event that the controller 34determines that a cycling event occurred (or in general that anaggressive driving event occurred), the controller 34 may store that inits memory along with the driver identification information. If thecontroller 34 determines that this particular driver has too manyinstances of aggressive driving, the controller 34 may make changes tothe criteria that would trigger the controller 34 to put the tensionerin a high tension setting whenever it senses that that driver is drivingthe vehicle. Another way that the vehicle may identify the driver is bythe key fob. In some luxury vehicles today, the vehicle's controller iscapable of distinguishing one key fob from another. The vehicle'scontroller uses this information to adjust the seats, mirrors and thelike to each driver's preferences based on which key fob is sensed. Thusthe controller 34 may be able to determine which driver is driving thevehicle based on which key fob is being sensed by the vehicle's sensors.

Further with respect to reducing the tendency of the tensioner actuator28 to hunt continuously, the tensioning system controller 34 may beprogrammed to may raise or drop the belt tension by discrete amounts asopposed to continuously adjusting it to achieve the optimal belt tensionfor dynamic (i.e. continuously changing) conditions. The tensioningsystem controller 34 may be programmed for this to occur always, oralternatively it may be programmed for this to occur only under certainconditions, while permitting hunting (i.e. continuous adjustment of thebelt tension) under other conditions. An example of the use of adiscrete change in belt tension is in a situation where the tensioningsystem controller 34 detects a constantly increasing required belttension. In such a scenario the tensioning system controller 34 maydecide to increase the belt tension to a selected high setting and toleave it there for a period of time, (unless it becomes necessary toincrease it further), instead of continuously adjusting the belt tensionto just match the necessary tension for each instant of time.

In another scenario, the tensioning system controller 34 may detect asituation where the engine speed is low (i.e. below a selectedthreshold). Resonance can occur in the belt 14 depending on certainfactors, such as the engine speed, the load on the belt 14 and the belttension. Resonance can cause the belt 14 to flutter and can in somesituations cause damage to or failure of the belt 14. In particular,some belts that are proposed for use or are in use in vehicles today arerelatively thinner than some belts previously used, which makes themeven more prone to flutter. To inhibit this from occurring thetensioning system controller 34 may be programmed to detect situationswhere the engine speed and belt load would lead to an increased risk ofresonance at a given belt tension, and to increase the belt tension soas to reduce the risk of belt flutter.

As shown in the examples described above, the tensioning systemcontroller 34 may thus be capable of predicting situations in which beltslip may be imminent, or in which increased belt load may be imminentand may be able to control the belt tension before these events takeplace.

As described above, the tensioning system controller 34 can control thetensioning force by the pulley 22 on the belt 14 so as to reduce thebelt tension where possible and to increase the belt tension whenneeded. This provides an overall improvement in fuel economy for thevehicle, as compared to a tensioner that is not controllable. However,this is, in some ways, a passive approach to reducing belt tension toimprove fuel economy (which may be referred to as fuel efficiency). Insome embodiments, the tensioning system controller 34 may take an activeapproach to reducing belt tension to improve fuel economy.

For example, the tensioning system controller 34 may be operativelyconnected to one or more of the alternator 16, the air conditioningcompressor 18 and any other accessories driven by the belt 14. It willbe understood that each of these accessories represents a load on thebelt 14, and each requires a certain amount of belt tension to operatewithout belt slip. By having two of these loads operate at the sametime, as can commonly occur, the belt tension must be increased furtherin order to reduce the likelihood of slip. In an effort to reduce themaximum belt tension required to be applied by the tensioner, thetensioning system controller 34 may in some situations cause a reductionin the load associated with one of the accessories, when permittinganother of the accessories to operate. For example, the tensioningsystem controller 34 may determine that the alternator 16 need notoperate at its highest voltage (which increases the amount of magneticdrag is associated with the alternator 16) when the air conditioningcompressor 18 is on. Thus, the tensioning system controller 34 mayreduce the voltage of the alternator 16 at those times if possible, andmay possibly shut off the alternator altogether. Similarly, thetensioning system controller 34 may reduce the refrigerant flow to theair conditioning compressor 18 (or may shut if off entirely) when itdetermines that the alternator 16 needs to run at high voltage. It willbe noted that some alternator types (e.g. some modern high efficiencyalternators) have a relatively high amount of drag associated with themin cold weather. This is due, at least in part, in some circumstances tothe close tolerances that exist between the rotating and stationarycomponents of such alternators. In cold weather, differential amounts ofshrinkage of some components relative to each other can increase theamount of rotational friction that exists until the alternator warms up.Furthermore, when the vehicle sits idle (i.e. when the vehicle is off)for any period of time (even overnight) during cold weather, thevehicle's battery can lose charge relatively quickly, thereby causingthe alternator 16 to operate at high load at vehicle startup as itattempts to charge the battery. As such, the tensioning systemcontroller 34 may prevent the alternator 16 from operating duringstartup of the engine 13 in cold weather since engine startup alreadyintroduces a high belt load which implies a raised belt tension. Oncethe engine 13 has started up and the belt tension necessary to preventslip is reduced, the tensioning system controller 34 may permit thealternator 16 to start up. In some embodiments, the controller 34 mayprevent alternator 16 from operating until the temperature of thealternator 16 reaches above a selected temperature. A temperature sensorthat is directly responsible for sensing the temperature of thealternator 16 may be provided for informing the controller 34 of thealternator temperature. If it is determined that the alternator 16 isneeded to operate but is below a selected temperature, the controller 34may put the tensioner at a high tension setting prior to start up of thealternator. The selected temperature below which the alternator 16 maybe considered to be cold may be for example, less than or equal to about−20 degrees C. Optionally, this condition (the low alternatortemperature) may override other logic used by the controller 34 tomodify belt tension. In other words, the controller 34 may be programmedto generate a high belt tension whenever it detects that the alternatortemperature is below the threshold value (assuming that alternatoroperation itself is needed), and to hold the high belt tension until thealternator temperature rises above a second threshold value, such as,for example, +20 degrees C.

With respect to the alternator 16, it is beneficial for the controller34 to be able to estimate the torque needed to drive the alternator 16in order to determine whether to change the belt tension. The alternatortorque depends on several factors, including voltage, current and speed.These values can be mapped to estimate torque quickly and easily withoutsignificant computational requirements. The controller 34 can use thisestimate to determine what belt tension is suitable.

It will be noted that the operative connection between the tensioningsystem controller 34 and the accessories may not be a direct one. Forexample, the tensioning system controller 34 may send instructions tothe vehicle control unit 32 to stop or prevent operation of thealternator 16, and the vehicle control unit 32 may determine whetherthis is possible. For example, the vehicle control unit 32 may determinethat it is not possible due to a critically low state of charge of thevehicle battery (not shown). In such an instance, the vehicle controlunit 32 may send a signal back to the tensioning system controller 34that it cannot stop, slow down or prevent operation of the alternator16, in which case the tensioning system controller 34 may drive up thetensioning force accordingly. Overall, however, by providing somecontrol over the accessories, the tensioning system controller 34 may beable to reduce the number of times the tensioning force needs to bedriven up to high levels. The number of times that the tensioning forcereaches high levels directly impacts the size of the shafts, bearingsand brackets required for the various components associated with theaccessories, so that they are sufficiently robust to resist deformationand fatigue. Reducing the number of times that the tensioning forcereaches high levels can therefore result in the use of relativelysmaller shafts, smaller and/or lighter-duty bearings, and lighterbrackets. This reduction in weight of the components in turn results inan increase in fuel efficiency for the vehicle, and reduces rotationaldrag associated with the accessories which can result in a furtherincrease in fuel efficiency for the vehicle.

Instead of sending instructions to the vehicle control unit 32, it isalternatively possible for the tensioning system controller 34 todirectly send commands to one or more of the accessories. However, thevehicle control unit 32 may also be directly or indirectly operativelyconnected to the accessories, and it may issue overriding commands tothe tensioning system controller 34 under certain conditions whichprevent the tensioning system controller 34 from interfering with thevehicle control unit's operation of the accessories.

The tensioning system controller 34 may receive signals from one or morecomponents that are indicative of the current belt tension so that thetensioning system controller 34 can determine if the current belttension is suitable or not for the current set of conditions. Thesignals may be from a position sensor that indicates the position of thesecond end of the tensioner spring, which gives an indication of thetensioning force exerted by the pulley 22 on the belt 14. The positionsensor could be a simple Hall-effect sensor which would send a signalproportionate to the distance between the sensor and the end of thespring. A suitable Hall-effect sensor could be a Honeywell SS 520sensor, supplied by Honeywell International, whose headquarters are inMorristown, N.J., USA. Alternatively other more precise position sensingdevices could be used, albeit at greater cost. Alternatively, the belttensioning system may include other, more sophisticated devices, suchas, for example, a strain gauge on one or more accessory shafts alongwith associated electronics for conditioning and signal amplification.Such devices are typically relatively high cost however. Such a deviceis described in U.S. Pat. No. 6,216,547 which is hereby incorporated byreference.

While the tensioning system controller 34 is shown as a separate devicefrom the vehicle control unit 32, it is possible to provide theequivalent of the tensioning system controller 34 within the vehiclecontrol unit 32 itself. In other words the tensioning system controller34 could be a program module that resides in memory along with theprogram module that makes up the vehicle control unit 32. For thepurposes of the claims provided below, however, the tensioning systemcontroller 34 and the vehicle control unit 32 may nonetheless beconsidered to be separate elements regardless of whether they sharehardware or even some software elements.

In a particular embodiment shown in FIGS. 3 a and 3 b, the vehicle maybe equipped with technology that shuts off the engine 13 temporarily incertain situations to reduce emissions and increase fuel efficiency. Forexample the vehicle control unit 32 may shut off the engine 13 when thevehicle stops at a stoplight. When this occurs it may still be desirableto continue operation of one or more of the belt driven accessories,such as the air conditioning compressor, for example. To achieve this,the crankshaft 10 may be equipped with a crankshaft clutch 38 throughwhich it connects to the crankshaft pulley 12. By disengaging the clutch38 the belt 14 can now be driven without the engine 13 turning. Thevehicle control unit 32 may be programmed to run the alternator 16 as amotor, which draws power from an electrical source such as the vehiclebattery (not shown). The motor 16 can then drive the belt and the otherbelt-driven accessories. Such a system is described in WO2008/113186A1,which is hereby incorporated by reference. It will be noted that inFIGS. 3 a and 3 b, only the components directly engaged with the belt 14are shown, such as the crankshaft 10 and related components, theaccessories and related components and the tensioner 20. Also, a waterpump is shown at 55 in FIGS. 3 a and 3 b as one of the accessories. Thedifference between the embodiments shown in FIG. 3 a and the embodimentshown in FIG. 3 b is that the tensioner 20 in FIG. 3 a is a lineartensioner (as shown in FIG. 1 a), and the tensioner 20 shown in FIG. 3 bis a rotary tensioner (as shown in FIG. 1 b).

In such an embodiment, the tensioning system controller 34 may receive asignal from the vehicle control unit 32 indicating that the engine 13 isbeing shut off and may be programmed to reduce the belt tension to a lowlevel so as to reduce the belt load, thereby increasing the amount oftime the battery can support rotation of the motor 16. As a further stepto reducing the belt load the tensioning system controller 34 may alsoreduce the refrigerant flow to the air conditioning compressor 18 to arelatively low level so as to reduce the belt load associated with thecompressor 18.

Alternatively, if flow reduction is not possible, the tensioning systemcontroller 34 may attempt to mimic the reduction or the throttling ofthe flow of fluid by intermittently cycling the air conditioningcompressor clutch on and off in a controlled fashion via a PWM pulsewidth modulation control strategy, or PPM, whereby the cycle time offand the cycle time on may be varied to optimize both the power savingspotential as well as the cooling potential within the passengercompartment.

In such an embodiment, the motor 16 may also be used to start the engine13. To carry this out, the crankshaft clutch is engaged so that thecrankshaft pulley 12 and the crankshaft 10 rotate together, and themotor 16 drives the belt 14 in order to drive the crankshaft 10, therebyreplacing a traditional starter motor. However, it will be noted thatthe crankshaft pulley 12 is positioned on a first side (shown at 40) ofthe motor pulley 54. When the motor pulley 54 drives the belt 14, thefirst side of the motor pulley 54 is the slack side. Thus the belttension on the first side 40 is relatively lower than the belt tensionon the second side (shown at 44) of the motor pulley 54. The lower belttension introduces some potential for slip to occur between the belt 14and the crankshaft pulley 12. It is possible to add a tensioner for thebelt span between the motor pulley 54 and the crankshaft pulley 12,however this is an expensive solution. In order to reduce the risk ofslip when only one tensioner is provided (i.e. tensioner 20) thetensioning system controller 34 may use the tensioner 20, which, as canbe seen is positioned between the crankshaft pulley 12 and the airconditioning compressor pulley 60, to increase the belt tension to avery high level so as to drive up the tension in the belt span (or beltspans) between the crankshaft pulley 12 and the motor pulley 54 so as toreduce the likelihood of slip during starting of the engine 13 using themotor 16. To assist in distributing the tension applied by the tensioner20 throughout the belt 14 more evenly, one or more of the accessoriesmay be shut off by the tensioning system controller 34 when the motor 16is used to start the engine 13. Once the engine 13 has been started, themotor 16 may revert back to an alternator, the belt tension may bereduced and whatever accessories were shut off may be started up again.Increasing the belt tension has been described as being applicableduring startup of the engine 13 by the motor 16, while the tension hasbeen described as being reduced by the controller 34 when the motor 16is driving the accessories. However, in a case where an accessory thatis on the slack side of the motor pulley 54 (e.g. the water pump 55) isdetermined to be necessary to operate without slip, the tension in thebelt 14 may be increased by the controller 34 to facilitate it.

While the alternator 16 has been described as being the motor thatdrives the belt 14 to drive the other accessories or to start the engine13, it is alternatively possible for a motor to be provided that isseparate from the alternator 16 for this purpose.

Many of the scenarios described above relate to the controller 34detecting a situation where increased belt tension may be required toprevent slippage from occurring, it may be possible for the controller34 to detect upcoming situations where low belt tension may bepermitted. For example, after detecting that the belt 14 potentially haddew on it and increasing the belt tension accordingly to prevent slip,the controller 34 may set a fixed period of time for the increased belttension to occur, and, in the absence of other reasons to keep the belttension up, the controller 34 may be programmed to reduce the belttension automatically at the end of the fixed period on the assumptionthat the belt 14 is dry at that point.

Some systems of the prior art may adjust belt tension based on adetermination that the current conditions are conducive to belt slip.However, this inherently means that there is a period of time duringwhich the conditions exist and where belt slippage could occur prior tothe system increasing belt tension. By detecting the potential for suchsituations before they occur (i.e. precognitively), the controller 34 isable to increase the belt tension before the need for increased belttension arises, thereby avoiding a situation where slippage has alreadyoccurred before the tensioning system has had a chance to react.

Many parameters have been described herein as being useful for use bythe controller 34 to determine the appropriate tension setting for thetensioner. All of these parameters may be combined into a map that maybe stored in the controller memory. The controller 34 would thendetermine all the necessary inputs based on signals from sensors, fromthe vehicle ECU, and/or from other sources, and may then use thoseinputs with the map to determine a tension to apply to the belt 14,and/or a tensioner mode for the controller 34. An example of a tensionermode would be a situation where the controller 34 has determined thatthe tensioner is hunting and then holds the tensioner at a particulartension setting for a set period of time to prevent it from hunting.Another example of a tensioner mode would be a situation such as duringstartup of the vehicle, whereby the tensioner may simply leave thetensioner at a high tension setting for a selected period of time,regardless of what signals are coming from the various sources.

While the term ‘belt’ has been used in the description herein, it willbe understood that the tensioning system of the present invention canapply to many different kinds of endless drive element, both synchronous(e.g. toothed) and asynchronous (e.g. non-toothed), including accessorydrive belts, timing belts, timing chains and the like.

Reference is made to FIGS. 4 a-4 c and 5 a-5 c, which show a tensioner200 with an example of a tension adjustment system in accordance withanother embodiment of the present invention.

The tensioner 200 includes a hub 221 that mounts to the engine 13, atensioner arm 224 that is rotatably supported by an arm bushing 225 onthe hub 221 for rotation about a hub axis between a free arm stopposition and a load stop position, and which holds a tensioner pulley222 for rotation about a pulley axis Ap, a tensioner biasing member 226(which may be referred to as a spring 226 or a torsion spring 226, butwhich could be any suitable type of biasing member) for biasing thetensioner arm 224 towards the free arm stop position, and a tensioneractuator 228 which is operatively connected to the tensioner pulley 222and tensioner arm 224 to change the tensioning force applied by thetensioner arm 224 on the belt 14 through the pulley 222.

In the embodiment shown in FIGS. 4 a-4 c and 5 a-5 c, the tensioneractuator 228 is made up of a motor 230, in this instance with anintegral gearbox, a worm 232, a sector gear 234 driven by the worm 232,and a spindle 236. The worm 232 is supported on bushings 238 in abracket 240 that is part of the hub 221, and is driven by the motor 230,which is controlled by the controller 34. The worm 232 causes rotationof the sector gear 234, which is connected to the spindle 236 viaprojections 242. The spindle 236 includes a driver slot 244 in itthrough which a spring tang 246 formed at the first end 248 of thespring 226. The second end of the spring 226 is shown at 250 and engagesthe tensioner arm 224. Rotation of the spindle 236 therefore causesrotation of the first end 248 of the spring 226. In a low tensionsituation, the tensioner 200 may engage the belt 14 with the arm 224positioned as shown in FIG. 5 a. Rotation of the first end 248 in afirst direction 252 causes the biasing force of the spring 226 on thetensioner arm 224 to increase progressively, thereby increasing thetensioning force of the tensioner arm 224, or more specifically thepulley 222, on the belt 14. Increasing the tensioning force causesrotation of the arm 224 in the clockwise direction in the views shown inFIG. 5 a-5 c, until the tension in the belt 14 increases sufficientlythat an equilibrium is reached between the tensioner arm 224 and thebelt 14. FIGS. 5 b and 5 c show the tensioner 200 when the tensioningforce has been increased from the low tension setting in FIG. 5 a, tomidlevel tension setting (FIG. 5 b), and to a high tension setting (FIG.5 c) respectively. It will be noted that the flights of the worm 232 arepreferably configured to prevent the worm from being backdriven by thesector gear 234 so that when there is high tension in the belt 14, thebiasing member 326 cannot relieve itself by backdriving the worm 232. Ifthe rotation is in a second direction shown by arrow 254 in FIG. 4 a,the tensioning force applied to the belt 14 is reduced progressively.

The tensioner 200 is provided with two sensors shown at 260 and 262respectively. The sensor 260 is provided for measuring the speed of thepulley 222 and may be similar to the sensor 72 shown in FIG. 2 a. Thesensor 262 is provided for measuring the position of the tensioner arm224. The sensor 262 may be any suitable type of sensor. For example itmay be an angular position sensor, which is stationary and which candetect changes in the angular position of a circular magnet 264 which isconnected for rotation with the tensioner arm 224 and is aligned withthe hub axis Ah (FIG. 4 b). The magnet 264 has a north pole that makesup 180 degrees of the magnet, and a south pole that makes up the other180 degrees. The position sensor 262 may be any suitable type of sensorthat can detect the change in the position of the north and south polesof the magnet 264 as the arm 224 pivots about the hub axis Ah. Anexample of a suitable sensor is a model 2SA-10 Sentron sensor providedby Sentron AG, of Zug, Switzerland. A suitable position sensing system(made up of a sensor like sensor 262 and a circular magnet like magnet264) is shown and described in U.S. Pat. No. 7,188,021, which isincorporated herein in its entirety. Instead of providing two sensors260 and 262 in the tensioner 200, it would be possible to omit one ofthe sensors 260 or 262, or to provide the tensioner 200 with neither ofthe sensors 260 or 262.

Another sensor (not shown) may be provided to determine the position ofthe first end 248 of the biasing member 226.

The information from the sensors may be sent to the controller 34 whichmay be programmed to use the pulley speed information from sensor 260 todetermine the speed of the belt 14, which the controller 34 can use whendetermining if there is any belt slip at one or more of the accessorypulleys or crankshaft pulley engaged with the belt 14. The informationfrom sensor 262 may be used by the controller 34 to determine theprecise position of the tensioner arm 24 which the controller 34 can useto determine the tensioning force being applied to the belt 14 andtherefore the tension in the belt 14. The controller 34 can use thisinformation as feedback to assist it in controlling the actuator 222 inorder to apply a selected amount of tension in the belt 14 using any ofthe algorithms described herein.

Reference is made to FIGS. 6 and 7 a-7 c, which describes a tensioner300 in accordance with another embodiment of the present invention. Thetensioner 300 may have a hub 321, a tensioner arm 324 that has a pulley322, a biasing member 326 that drives the arm 324 towards the free armstop position, and an actuator 328 that drives a spindle 336 that drivesone end of the biasing member 326 to control the biasing force, andtherefore the tensioning force, and therefore the belt tension. All ofthese components may be similar to their counterparts, 221, 222, 224,226, 228 and 236 shown in FIGS. 4 a-4 c, except that the tensioner arm324 has a projection 370 that extends downwards into a slot 372 on thespindle, shown at 336. Referring to FIGS. 7 a-7 c, FIG. 7 a shows thetensioner 300 at a low tension setting. It will be noted that all of thetensioner arm 324, except for the projection 370 has been omitted fromFIGS. 7 a-7 c so as to show the projection 370 and the slot 372 moreclearly. As can be seen in FIG. 7 a, at this setting, the projection 370is roughly in the middle of the slot 372, spaced from both ends, shownat 374 and 376 of the slot When the controller 34 determines that thebelt tension should be raised, the motor shown at 330 drives the worm332, which drives the sector gear 334, which drives the spindle 336,which drives the first end 348 of the biasing member 326 therebyincreasing the biasing force of the biasing member 326 on the tensionerarm 324. This causes the tensioner arm 324 to rotate as it presses withmore tensioning force into the belt 14. FIG. 7 b shows the tensioner arm324 at a midlevel tension setting. It will be noted that in FIG. 7 b,the projection remains spaced from both ends 374 and 376 of the slot372. As the controller 34 continues to drive the first end 348 of thebiasing member 326, the first end 348 of the biasing member 326 willrotate angularly towards the second end shown at 350. If there is toomuch angular rotation of the first end 348 towards the second end 350,it may be possible that the biasing member 326 could become damaged. Toprevent this, as the first end 348 rotates towards the second end 350,the first end 374 of the slot 372 on the spindle 336 rotates towards theprojection 370. If the first end 348 of the biasing member 326 rotatesby a selected angular amount towards the second end 350, the first end374 of the slot 372 engages the projection 370. At this point, if theactuator 328 continues to drive the rotation of the first end 348 of thebiasing member 326, the projection 370 (and therefore the tensioner arm324) will be driven to rotate by the first end 374 of the slot 372 sothat the relative angle between the first and second ends 348 and 350 ofthe biasing member 326 cannot decrease any further. Because the relativeangle between the first end 348 and second end 350 of the biasing member326 no longer decreases with further rotation of the sector gear 334,the biasing force applied by the biasing member 326 to the tensioner arm324 no longer increases. However, because the tensioner arm 324continues to be driven further and further into the belt 14 with furtherrotation of the sector gear 334 (by the motor 330), the tension in thebelt 14 continues to increase. FIG. 7 c shows the tensioner arm 324 at ahigh tension setting where the projection 370 engages the first end 374of the slot 372.

It will be noted that the projection 370 could instead be on the spindle336 and the slot 372 could instead be on the tensioner arm 324. It willbe further noted that there need not be a slot at all for engaging theprojection 370. For example, a first projection could be provided on thespindle 336 that extends radially outwards and upwards. A secondprojection could be provided on the tensioner arm 324 and could extendradially outwards, or optionally radially outwards and downwards. Afirst engagement surface on the first projection would engage a secondengagement surface on the second projection if the relative anglebetween the first and second ends of the biasing member decreases belowa selected angle, thereby preventing any further decrease in therelative angle.

The tensioner 300 may includes sensors similar to sensors 260 and 262 inthe embodiment shown in FIGS. 4 a-4 c.

Reference is made to FIGS. 8 a, 8 b, 9 a and 9 b, which shows atensioner 400 in accordance with another embodiment of the presentinvention. The tensioner 400 may have a hub 421, a tensioner arm 424that has a pulley 422, a biasing member 426 (FIG. 8 b) that drives thearm 424 towards the free arm stop position, and an actuator 428 that mayall be similar to the components 221, 224, 222, 226 and 228 shown inFIG. 4 a-4 c, except that the actuator 428 does not drive the first endshown at 448 of the biasing member 426, and instead drives a spindle 436that drives a bumper arm 475 that includes a second biasing member 476and a cover 477, into a projection 478 on the tensioner arm 424 to drivethe tensioner arm 424 (more specifically the pulley 422 on the tensionerarm 424) into the belt 14, thereby controlling the tensioning force, andtherefore the belt tension. FIG. 9 a shows the tensioner in an unboostedstate. This may be considered a low tension setting, and the firstbiasing member 426 may be selected to have a spring constant that isrelatively low for this purpose and may be configured to exert arelatively low biasing force on the tensioner arm 424 for this purpose.In this state the bumper arm 475 is unengaged with the projection 478 onthe tensioner arm 424 and so the tensioner 424 operates as a typicaltensioner according to the response curve 102 shown in FIG. 1 c. It willbe noted that in this state, the bumper arm 475 is sufficiently out ofthe way that the tensioner arm 424 can pivot throughout a desired rangeof motion without engagement between it and the bumper arm 475.

When it is desired to boost the tension in the belt 14, the motor shownat 430 drives worm 432, which drives sector gear 434, which drivesspindle 436 to bring the bumper arm 475 into engagement with theprojection 478 on the tensioner arm 424 (shown in FIG. 9 b), so as tourge the tensioner arm 424 into the belt 14 to increase the tension inthe belt 14. Once engagement between the bumper arm 475 and thetensioner arm 424 occurs, further rotation of the motor 430 results in aprogressively greater amount of compression of the second biasing member476, which increases the amount of force it applies to the tensioner arm424. This in turn increases the tensioning force applied by thetensioner arm 424 on the belt 14 which in turn increases the belttension. Because the motor 430 is only engaged with the tensioner arm424 through the second biasing member 476, the tensioner arm 424 canstill pivot to accommodate dynamic fluctuations in belt tension evenwhen the tension is being boosted, or more broadly, even when thetensioner arm 424 is engaged by the bumper arm 475.

Referring to FIG. 9 b, a moment arm M1 exists between the line of actionthrough the pulley axis Ap of the pulley 422 and the pivot axis Ah ofthe tensioner arm 424. A moment arm M2 exists between the line of actionof the bumper arm 475 on the projection 478 and the pivot axis Ah. It isoptionally possible to configure the tensioner 400 so that the momentarm M2 is greater than the moment arm M1 so as to facilitate driving thepulley 422 into the belt 14 against the force exerted by the belt 14 onthe pulley 422.

The tensioner 400 may include one or more sensors. A sensor shown at 460may be similar to sensor 260 and is used for determining the speed ofthe pulley 422. A sensor shown at 462 may be similar to sensor 262 andis used for determining the position of the tensioner arm 424. A sensorshown at 465 is provided for determining the force applied by the secondbiasing member 476 on the tensioner arm 424, which is used in additionto the information from the sensor 462 which provides tensioner armposition information and therefore information regarding the forceapplied on the arm 424 by the first biasing member 426, so as todetermine the tensioning force being applied to the belt 14. This can beused as feedback for the controller 34 while driving the motor 430 toboost the belt tension, in order to determine at what position to stopthe motor 430. The sensor 465 may be, for example, a button load cellmounted to the cover 477. Instead of the sensor 465, the bumper arm 475may contain a displacement measurement sensor 466, which can be used tomeasure the length of the bumper arm 475, thereby indicating the amountof compression there is in the second biasing member 476. This can beused by the controller 34 to determine the force exerted by the secondbiasing member 476 on the projection 478, which can be used to determinethe overall tensioning force applied by the tensioner 400 on the belt 14and thereby determine the belt tension. The displacement measurementsensor 466 may be configured to signal the controller only when inextended and retracted positions, or may be configured to signal to thecontroller 34 when it reaches any of three or more positions.

When it is desired to position the tensioner 400 in a low tensionsetting, the motor 430 may be rotated in the opposite direction as whenboosting tension. When the controller 34 detects that the sensor 465 nolonger senses any engagement between the bumper arm 475 and theprojection 478, the controller 34 may be programmed to rotate the motor430 by a selected number of revolutions to bring the bumper arm 475sufficiently out of the way to accommodate the pivoting of the tensionerarm 424 when operating at the low tension setting.

It will be noted that, in the embodiment shown in FIGS. 8 a, 8 b, 9 aand 9 b, the element that holds the first end of the biasing member 426is fixedly mounted to the hub 421 so that the first end of the biasingmember 426 remains stationary and is not rotated with the spindle 436.

Reference is made to FIG. 10, which shows a tensioner 500 in accordancewith another embodiment of the present invention, which includes a hub521, a pulley 522, a tensioner arm 524, a biasing member 526 and anactuator 528, which is controlled by controller 34. The actuator 528includes, among other things, a motor 530, a worm 532, a sector 534 thatis connected for rotation with a spindle 536. The tensioner 500 may besimilar to the tensioner 400 except that in the tensioner 500, theelement that holds the first end of the biasing member shown at 526 ispart of the spindle (shown at 536). FIG. 11 a shows the tensioner 500 ata low tension setting. In this state, the bumper arm shown at 575, whichmay be similar to bumper arm 475, is out of the way of the projectionshown at 578 on the tensioner arm 524 so that the tensioner arm 524 canpivot throughout some range of motion as a result of engagement with thebelt 14 without contacting the bumper arm 575. FIG. 11 b shows thetensioner 500 at a high tension setting. To boost the tension in thebelt 14, the bumper arm 575 is driven by the motor shown at 530 towardthe projection 578. This drives the first end 548 of the biasing member526 however, which increases the torsion in the biasing member 526, andtherefore drives the tensioner arm 524 to rotate further into the belt14, increasing the belt tension. At some point, the spindle 536 isrotated sufficiently relative to the tensioner arm 524 that the bumperarm 575 engages the projection 578. At that point, further driving ofthe spindle 536 drives the bumper arm 575 further into engagement withthe projection 578 which increases the biasing force applied by thebiasing member 526, and which also increases the biasing force appliedby the second biasing member shown at 576 which is part of the bumperarm 575. This assists in preventing damage to the first biasing member526 resulting from overrotation of the first end 548, because thepresence of the bumper arm 575 provides assistance so that a selectedbelt tension can be reached without all of the force having to begenerated through the first biasing member 526. The remote drivearrangement shown for the tensioner 500 may be applied to any of thetensioners shown and described herein where a motor is utilized andwould benefit from being positioned away from the engine block.

The tensioner 500 may includes sensors similar to the sensors 460, 462and 465 shown in FIGS. 8 a and 8 b and a displacement measurement sensorsimilar to displacement measurement sensor 466.

Reference is made to FIG. 12, which shows a tensioner 600 in accordancewith another embodiment of the present invention. In a situation wherethe temperature in the immediate environment of the motor is high, theoperating efficiency of the motor decreases, sometimes significantly.This is due to several factors, including the fact that the resistanceof the copper wire in the motor increases with temperature. Thus at 60degrees Celsius or at 80 degrees Celsius, the wire has a higherresistance than it does at 25 degrees Celsius. As a result, the torquecapability of the motor is reduced at high temperature. To compensatefor this the motor may have to be upsized significantly in order to beassured of being able to handle a given torque requirement. To assist inkeeping the cost of the motor shown at 630 low, the tensioner 600 may besimilar to the tensioner 200 except that the tensioner 600 includes aremote drive arrangement in that the motor 630 is operatively connectedto the worm 632 through a flexible shaft 680. The flexible shaft 680permits mounting the motor 630 away from the engine block, which meansit may be possible to keep the motor 630 at a lower temperature than onethat is mounted to or proximate to the engine block. The motor 40 may bepositioned in a particularly cool part of the engine bay, such as nearthe grill or at some other cool air inlet. This would permit a lessexpensive motor to be used since it would not need to be oversized tocompensate for a reduction in efficiency resulting from operatingtemperature.

Also, in any of the embodiments wherein a motor drives either the tangof the biasing member or drives a bumper arm, a locking mechanism (notshown) can be brought into provided to lock the spindle in a particularposition. The locking mechanism may include a pawl or the like thatengages an aperture or a detent or the like in the spindle. The spindlemay include only a single aperture or detent, and is thus only held whenit reaches a certain position, or it may have a plurality of pluralityof apertures or detents about its circumference so that it can be heldin a plurality of different positions. An actuator, such as a solenoid,would be provided to withdraw the pawl from the aperture/detent topermit the spindle to move to a different position or to return to ahome position. Instead of this, the locking mechanism could include acam that engages the tensioner arm, a wrap spring or any other suitablemeans.

If a gearbox is provided (as shown at 682) to reduce the speed andincrease the effective torque provided by the motor 630, it ispreferable that the gearbox be provided at the outlet end of theflexible shaft 680 (i.e. between the flexible shaft 680 and the wormshown at 632), as opposed to providing the gearbox between the motor 630and the flexible shaft 680. As a result, the flexible shaft 680 is notrelied upon to transmit high torque, which can result in its prematurewear and/or windup in the flexible shaft 680. The remote mounting of themotor 630 permits the motor 630 to be positioned in a particularly coolpart of the engine bay, such as near the grill or at some other cool airinlet.

Reference is made to FIG. 13 a, which shows a tensioner 700 inaccordance with another embodiment of the present invention. Thetensioner 700 includes a hub 721, a tensioner arm 724 that is pivotableabout a hub axis Ah, a pulley 722 mounted on the tensioner arm 724 forrotation about a pulley axis Ap, a biasing member 726 engaged betweenthe hub 721 and the tensioner arm 724 to bias the tensioner arm 724towards the free arm stop position, and a tensioner actuator 728. Thetensioner arm 724 shown in FIG. 13 a includes a central portion 724 aand an extendable portion 724 b that is extendable from the centralportion 724 a by the actuator 728. A motor 730 that is mounted on thecentral portion 724 a and drives a lead screw 790, which in turn causeslinear movement of a traveler 792 mounted at one end of the tensionerarm 724. This linear movement causes extension or retraction of thetensioner arm 724 depending on the direction of rotation of the motor730. Referring to FIGS. 13 c and 13 d, changing the length of thetensioner arm 724 (shown at L) changes the moment arm between the pulley722 and the hub axis Ah, and also changes the hubload angle. Changingthese properties changes the tensioning force applied by the pulley 722on the belt 14, which depends at least in part on the moment arm M2 ofthe pulley 722 as compared to the moment arm M1 of the biasing member726. Thus, when the moment arm of the biasing member 726 is constant asshown in FIG. 13 a, reducing the length L of the tensioner arm 724increases the tension in the belt 14 because it increases the force ofthe pulley 722 acting on the belt 14. Similarly, extension of thetensioner arm 724 decreases the moment arm of the tensioner arm 724 onthe belt 14, which decreases the tension in the belt 14. The length ofthe tensioner arm 724 may be determined using any suitable type ofsensor, such as a Hall effect sensor that counts revolutions of theleadscrew 790. In order to stabilize the arm 724 during use, theextendable portion 724 b may be generally U-shaped (albeit with a veryshallow U in the embodiment shown in FIG. 13 b). To further stabilizethe arm 724, a clamping mechanism (not shown) may be provided whichremoves any play that exists between the extendable portion 724 b andthe central portion 724 a. It will be noted that any of the tensionersshown and described may include a damping member as is known in the artto dampen oscillations of the tensioner arm. The damping force from thedamping member is preferably proportional to the torque applied.

Reference is made to FIGS. 14 a and 14 b, which shows a tensioner 800 inaccordance with another embodiment of the present invention. Thetensioner 800 may be similar to the tensioner 200 except that thetensioner 800 includes an actuator 828 that includes a motor 830 thatturns a lead screw 890 which has a traveler 892 thereon. The traveler892 engages projections 894 on the spindle, shown at 836. The spindle836 engages the first end 848 of the biasing member 826 so as to controlthe biasing force of the biasing member 826 on the tensioner arm shownat 824. The tensioner 800 further includes a hub 821 that mounts to theengine. A pulley 822 is mounted for rotation on the tensioner arm 824.

Referring to FIGS. 15-28, a tensioner 910 for an endless drive member911 includes a cylinder 912 which includes a first housing 914 and afirst piston 916. The main cylinder 912 at least partially defines afluid chamber 918. The first piston 916 defines a first end of the fluidchamber 918. In the embodiment shown, a second housing 920 (which may bereferred to as a reservoir) is provided that is connected to the firsthousing 914 via a fluid passageway 922 having a selected resistance tofluid flow. The second housing 920 defines part of the fluid chamber918. A second piston 924 is movable in the second housing 920 anddefines a second end of the fluid chamber 918. The fluid in the fluidchamber 918 (during use) is preferably a substantially incompressiblefluid such as hydraulic oil. A first piston biasing member 926 ispositioned to bias the first piston 916 towards the extended position(FIG. 6). A second piston biasing member 928 such as a spring isoptionally provided, to assist in urging the second piston 924 intoengagement with the fluid in the fluid chamber 918, even though thiscould be accomplished with a gas in the second housing 920 instead ofthe spring. A second piston position control device 930 is provided tocontrol the position of the second piston. The control device 930 mayinclude a threaded rod 932 that engages a threaded portion 934 at theend of the second housing 920. The threaded rod 932 may be rotated inone direction to drive it in towards the second piston 924 or in anotherdirection to drive it away from the second piston 924. The threaded rod932 may be used to set a limit position for the second piston 924. Thislimit position may be chosen so that the second piston 924 can be pushedby the fluid in the fluid chamber 918 by some selected amount.Alternatively, the threaded rod 932 could be brought right up intoabutment with the second piston 924 (FIG. 4) so as to prevent the fluidfrom pushing the second piston 924 at all. Alternatively, the threadedrod 932 could be rotated to drive the second piston 924 forward by someselected amount, thereby forcing the first piston 916 towards theextended position.

The first piston 916 is pivotally mounted at an external end to a basestructure such as the engine block (not shown) about a cylinder pivotaxis ACYL. The external end of the housing 914 is pivotally connected toa lever arm 936 about a lever arm engagement axis ALAE. The lever arm936 is pivotally connected to the base structure (e.g. the engine block)about a lever arm pivot axis ALAP. A pulley 938 is rotatably mounted tothe lever arm 936. The pulley is engaged with the endless drive member911 to tension the endless drive member 911. In an alternativeembodiment, it is possible for the pulley 938 to be directly mounted tothe external end of the housing 914 and to omit the lever arm 936. Insuch an embodiment, the movement of the housing 914 would be constrainedin some way, such as by guides that force it to travel linearly.

The threaded rod 932 may be driven to rotate by a motor shown at 940optionally via a flexible shaft shown at 942. The motor 940 may befixedly mounted (e.g. to a base structure that is spaced from the engineblock) and the flexible shaft 942 may permit operative connection of themotor 940 to the threaded rod 932 even though the threaded rod 932 movesduring operation of the tensioner 910. By mounting the motor remotelyfrom the engine block it may be possible to keep the motor 940 at alower temperature than one that is mounted to or proximate to the engineblock. This would permit a less expensive motor to be used.Alternatively as shown in FIG. 14, the motor 940 may be mounted to thesecond housing 920, in which case a shaft that is flexible is notnecessary.

If a gearbox is provided to reduce the speed and increase the effectivetorque provided by the motor, it is preferable that the gearbox beprovided at the outlet end of the flexible shaft (i.e. between theflexible shaft 942 and the threaded rod 932), as opposed to providingthe gearbox between the motor and the flexible shaft 942. As a result,the flexible shaft is not relied upon to transmit high torque, which canresult in its premature wear and/or windup in the flexible shaft.

Where the motor 940 is positioned remotely from the second housing 920,the motor 940 may be positioned in a particularly cool part of theengine bay, such as near the grill or at some other cool air inlet.

The operation of the motor 940 may be controlled by any suitable controlsystem. A generic control system is shown at 43 in FIG. 15. The controlsystem 943 may be made up of one or more individual components (e.g. oneor more controllers). The control system 943 may include the main ECU ofthe vehicle, or it may be separate from the main ECU of the vehicle. Inan embodiment, the control system 943 may be a separate controller thatcommunicates with the ECU of the vehicle via a wiring harness or via aCAN bus. A number of suitable types of relationship may exist betweenthe ECU and any other controllers that together form the control system943. For example, the ECU may sometimes or may all the time be a masterto the other controllers in the control system 943.

The control system 943 may set the position of the threaded rod 932using the motor 940 based on any suitable set of parameters. The controlsystem 943 may, for example, drive the threaded rod 932 inwards to movethe second piston 924 so as to move the first piston 916 to provide aselected high tension in the belt 911 in some situations where thecontrol system 943 determines that the belt 911 is determined to be atrisk of slippage or if slippage has been detected. An example of such asituation is upon startup of the vehicle, particularly on a cold day.Another example of such a situation is upon startup during a BAS (BeltAlternator Starter) belt starting sequence, where high belt tension isrequired only during the initial motor/alternator belt startingsequence, to spin the engine crankshaft by the belt. Another example ofsuch a situation is during moments where there is high engineacceleration or deceleration.

The control system 943 may also drive the threaded rod 932 outwards to aposition where it permits the second piston 924 to travel freely in thesecond housing 920 where, for example, a lower tension is acceptable forthe belt 911 without risk of belt slippage. In some situations, thecontrol system 943 may drive the belt inwards so as to simply abut thesecond piston 924 so as to prevent the second piston from permittingcompression of the cylinder 912. This can be used during periods of beltflutter or belt resonance, during periods of high belt drive rotationtorsional acceleration (engine torsionals), or for example, duringsituations where a system disturbance (e.g. belt flutter) is anticipatedbased on inputs from one or more sensors, in order to prevent tensionloss/reduction due to the tensioner being forced back out of the beltduring such periods of instability.

The control of the motor 940 by the control system 943 may be open-loopor may be closed loop whereby the control system 943 receives inputsfrom one or more sensors that indicate whether the position of thethreaded rod 932 is as intended. Additionally the control system 943 mayreceive inputs from one or more other sensors which it uses to determinewhere to position the threaded rod 932. Such sensors may include, forexample, temperature sensor, a rain sensor, a sensor related to beltslip, and the like. Suitable algorithms for the control system 943 aredescribed in copending application 61/486,189, the contents of which areincorporated herein by reference.

The L-shaped configuration between the cylinder 912 and the secondhousing 920 facilitates rapid tuning using take apart components whichcan be switched out as required. However, an in-line configuration mayalternatively be provided. Furthermore, a monotube configuration may beprovided in which the entire fluid chamber and both the first and secondpistons are contained in a single cylinder housing. In a monotubeconfiguration, the connector at the external end of the housing could beshifted to the side so as to make room for the threaded rod to enterinto the housing through the end of the housing.

In an alternative embodiment, the piston 916 and housing 914 could bereversed, whereby the piston 916 is connected to the lever arm 936 andthe housing 914 is pivotally connected to the engine block.

In one aspect, the novel concept here is to block the return of thesecond piston to induce hydraulic lockout (piston lockout) therebypreventing, on demand, any retraction of the first piston 916 (i.e.compression of the cylinder 912) in response to a specific FEAD beltdrive system requirement.

In another aspect, the novel concept here is to drive the smallreservoir position in power mode, to extend (or retract) the strut toamplify the force by driving the first piston which may be larger thanthe second piston.

Different travel rates and load outputs can be achieved by manipulatingthe piston diameter ratios between the diameter of the first piston 916and the diameter of the second piston 924.

In some embodiments the connection between the first housing 914 and thesecond housing 920 could be separated by a flexible hose—a stiff flexsteel braided hose, for example, would probably be employed in such acase so as to minimize unwanted expansion of the hose under pressure,resulting in unwanted diametral elastic growth of the hose/tubing, whichwould ultimately result in adding an unwanted lag, or delayed response,to the final spring rate. Unwanted elasticity on the high pressure oilside is preferably eliminated in order to prevent force response lags,hence the use of non-elastic hoses where practical.

In the exemplary embodiment presented in the illustrations, the majorityof damping comes from the seals and damping rings installed within thefirst piston 916, as well as whatever damping comes from the flow offluid.

Extra damping can be added to the tensioner by introducing such devicesas a small orifice restriction and a blow off ball valve in the oil flowbetween the two housings, to induce restrictive orifice damping andsteady blow off damping.

In HYDRAULIC LOCKOUT MODE, the rod 932 merely stops the backward motionof the floating reservoir piston, which ultimately hydraulically locksthe larger piston 916 and prevents further insertion of the piston rodinto the cylinder housing 914, effectively locking the tensioner arm936.

In POWERED DRIVE MODE, the rod 932 is used to push the smaller floatingpiston 924, in order to force the larger tensioner cylinder piston 916to move in response to the flow of oil from the reservoir 20. Thetechnique, for example, may be used to push the pulley 938 harder intothe belt under conditions where belt slip would otherwise be imminent,such as during a BAS start (in hybrid vehicles), or during wet orextremely cold conditions.

The rod 932 used to lock out or drive the reservoir piston 924 can bedriven via a fine lead screw arrangement, as depicted in the figures, orit could be driven linearly (as opposed to the rotational actuationrequired by a lead screw arrangement) by a powerful linear solenoid—anyactuator device which is capable of blocking movement of the smallerreservoir piston 924 or of driving the reservoir piston 924 (in powereddrive mode described below) could be employed. The solenoid may actuatethe rod 932 linearly via a flexible cable (e.g. a Bowden cable). Thiswould permit the solenoid to be mounted remotely in a cooler spot in theengine bay, (e.g. near the grill) in similar manner to the remotemounting of the motor 940, described above. An example of a suitablesolenoid with a flexible cable arrangement that may be used in someembodiments is provided by Trombetta, which is owned by Fulham &Company, and is located at Menomonee Falls, Wis., USA.

It will be understood that, under typical conditions where temperatureis not an issue, it is preferred to mount the motor 940 or solenoid insubstantially direct engagement with the rod 932 (as opposed to a remotemounting with a flexible shaft or push/pull cable between them) so as toreduce the number of components between the motor 940 or solenoid andthe rod 932, so as to increase the torque transfer efficiency betweenthe motor 940 or solenoid and rod 932. However, in a situation where thetemperature in the immediate environment of the load will be high andthe motor is in that environment, the operating efficiency of the motordecreases, sometimes significantly. This is due to several factors,including the fact that the resistance of the copper wire in the motorincreases with temperature. Thus at 60 degrees Celsius or at 80 degreesCelsius, the wire has a higher resistance than it does at 25 degreesCelsius. As a result, the torque capability of the motor is reduced athigh temperature. To compensate for this the motor may have to beupsized significantly in order to be assured of being able to handle agiven torque requirement.

The threaded rod 932 is in a hot environment due to its proximity to theengine. By mounting the actuator (e.g. the motor 940 or the solenoid)remotely from the rod 932, the actuator can be placed in a coolerenvironment where its operating efficiency is not degraded, or notdegraded as much as it would be in the hotter environment. For example,the actuator may be placed near the grille of the vehicle where it isexposed to a strong airflow for cooling purposes.

Also a remote mounting of the actuator can be advantageous if there arespace and size limitations proximate to where the rest of the tensioner910 is mounted.

Instead of using a solenoid, a vacuum actuator can be used in someembodiments to drive the rod 932 linearly. The vacuum actuator may drawpower from the vacuum drawn from the air induction system. Vacuum drawnfrom the air induction system has been used in the past for otherpurposed such as to drive turbo waste gate motors and manifold inductionduct actuator motors, for example.

In some embodiments a pneumatic actuator may be used to drive the rod932 if a compressed air supply is available onboard the vehicle.Alternatively, a hydraulic actuator could be used, drawing power from asource of hydraulic fluid, such as the power steering system in vehiclesthat use a hydraulic power steering system, or, for example from theengine oil system. A compressed air supply, a hydraulic power supply, ora vacuum source are sometimes available on certain vehicles such astrucks and SUVs.

A vacuum actuator, a pneumatic actuator, or a hydraulic actuator may beswitched via a relatively inexpensive solenoid powered valve, and couldbe controlled electronically, via either an analog or digital signal,from the control system 943.

An example of a suitable actuator may be a door lock actuator, similarto (but perhaps scaled up in power and resistance to high temperature)those described in U.S. Pat. Nos. 6,067,826, 5,983,739, 5,634,676 thecontents of all of which are incorporated herein by reference. Such anactuator could be used successfully in some embodiments by incorporatinga gearbox with worm drive and a high gear ratio. Backdriving of such anarrangement can be prevented by the worm drive (in embodiments whereinit is provided) and/or by providing some other structure such as one ormore detent lock features, with a spring loaded lock and load feature asdescribed in U.S. Pat. No. 5,983,739, the contents of which are herebyincorporated by reference.

While a push-pull cable has been described as being usable in certainembodiments, other arrangements may be used, in addition to or insteadof a push-pull cable. For example a linkage may be used such as thelinkage shown in U.S. Pat. No. 5,634,676 the contents of which arehereby incorporated by reference, optionally with a push-pull cable.Using some linkages linear motion could be converted to rotary motion,or vice-versa. Such linkages may be used to alter the mechanicaladvantage by increasing force by reducing displacement, or by decreasingforce by increasing displacement, depending on the embodiment.

The first piston biasing member 926 may be a coil spring, as shown inthe figures, or it may be some other type of spring such as a closedcell foam (CCF) spring as shown in FIG. 27. It could alternativelyincorporate both a coil spring and a closed cell foam spring. An exampleof such a spring is supplied by BASF. An advantage to CCF springs isthat they can collapse to only 20% of their original height (vs 40% forsome steel coil springs). Another advantage to CCF springs is that it iseasy to manufacture them with a desired constant spring rate or a springrate that varies with the amount of compression of the CCF spring. Thismay be achieved by co-molding portions (e.g. layers) of the CCF spring,each having different properties. Properties that may be varied includedensity of the CCF, the cell size, the outer diameter and inner diameterof the CCF spring (in embodiments wherein they are hollow-cylindrical.Additionally you can easily tune their design to provide a selectedamount of energy dissipation. The shorter collapsed length of the CCFspring could be used to provide a larger linear travel of the cylinder912 for a given overall length of the cylinder 912. As anotheralternative, the first piston biasing member may include some other typeof biasing member such as, for example, one or more Belleville washers,one or more wave washers, gas pressure, or a combination of two or moreof these. All of these alternatives may also be used as the secondpiston biasing member 928 instead of or in addition to a coil spring.

In an example, the CCF spring may be used just as an end-of-traveljounce stop, to impart an elastically damped, super high spring rate atthe end of travel of a normal coil spring design. In another example,the CCF spring may be molded around metal coil springs or washer springsto impart new spring and new jounce stop properties to the overallspring assembly.

In an alternative embodiment shown in FIG. 25, the second piston biasingmember 928 may be positioned between the second piston 924 and a limitmember 944 that is in the second housing 920. The threaded rod 932engages the limit member 944. This structure is particularlyadvantageous when using the threaded rod 932 to set a limit for theamount of retraction that is possible for the first piston 916 in thefirst housing 914. With this structure, as the threaded rod 932 isadvanced into the second housing 920, it advances the limit member 944towards the second piston 924. This in turn causes the second pistonbiasing member 928 to compress, increasing its resistance to furthercompression. As a result, when the second piston 924 is moved to abutthe limit member 944 because of an increase in tension in the belt 911,the increased resistance offered by the biasing member 928 helps toreduce the abruptness of the engagement between the limit member 944 andthe second piston 924.

Reference is made to FIG. 26, which shows another embodiment of thepresent invention. In this embodiment, the tensioner includes a hub 946that is mountable to a base structure such as the engine block (notshown). A tensioner arm 948 is pivotable about the hub 946. The pulley938 is positioned at the end of the arm 948. A tensioning spring (notshown) and a damping element (not shown) are positioned about the hub946, as they are in a typical tensioner. The cylinder 912 is mounted insuch a way that one end (in this case the external end of the housing914) is pivotally mounted to a base structure, and the other end (inthis case the external end of the piston 916) is pivotally mounted tothe tensioner arm 948. The second housing 920 is provided, with thesecond piston 924 therein. In this embodiment, the threaded rod 932 isengageable with the second piston 924 only through the limit member 944and the second biasing member 928, however it is alternatively possibleto omit the limit member 944 and to provide an arrangement similar tothat shown in FIG. 24, wherein the threaded rod 932 directly engageablewith the second piston 924. The tensioner shown in FIG. 26 may actsubstantially like a typical tensioner. However, the additionalstructure including the cylinder 912 and related components, permits thetensioner arm 948 to be locked hydraulically as described above (ie. byengagement of the threaded rod 932 or limit member 944 so as to preventcomplete compression of the cylinder 912), and to be driven to adifferent (higher tension) position via the threaded rod 932 and asuitable actuator (eg. motor 940 and flexible shaft 942).

Reference is made to FIGS. 29 a and 29 b which show alternativestructures for locking the tensioner 910 and for boosting the tension inthe tensioner 910. A needle valve shown at 952 may be provided forcontrolling the flow of fluid between the first chamber portion shown at918 a and the second chamber portion shown at 918 b. The needle valve952 includes a flow control element 954 that is positionable in at leastan open position wherein flow through the passageway 922 is permittedand a closed position (FIG. 29 b) wherein flow through the passageway922 is prevented. The flow control element 954 may be positionable inonly those two positions (by means, for example, of a two-positionsolenoid) or alternatively it may be positionable in three or morepositions. In some embodiments it may be infinitely adjustable inposition via proportional control. When the flow control element 954 isin the closed position, the tensioner 910 is locked hydraulically inposition, in similar manner to the embodiment shown in FIGS. 15-28 inwhich the threaded rod 932 is adjusted to abut the second piston 924.When the flow control element 954 is in the open position it does notprevent the cylinder 912 from extending and retracting. When the flowcontrol element is positionable in one or more partially open positions,an example of which is shown in FIG. 29 a, it can be used as anadjustable orifice to control the rate of flow of fluid between thechamber portions 918 a and 918 b, thereby controlling the rate ofextension or retraction that is available to the cylinder 912 and actingas a damping member. While the threaded rod 932 is shown in FIGS. 29 aand 29 b it is not needed and the second housing 920 could simply have aclosed end instead.

Also shown in FIGS. 29 a and 29 b is an alternative tension boostmechanism shown at 955. The tension boost mechanism includes a fluidreservoir 956 and a pressure source 957, such as an electric pump. Thepressure source 957 connects to the chamber portion 918 b (oralternatively to somewhere else in chamber 918), via conduit 958. Whenit is desired to boost the tension, the pump 957 operates to pump fluidinto the chamber 918, forcing the second piston 914 backwards until thesecond biasing member 928 can no longer compress, and forcing thecylinder 912 to extend to drive the pulley 938 into the belt 911. When adesired tension is reached in the belt a valve (not shown) in conduit958 can be closed which would still permit the tensioner 910 to extendand retract, or alternatively, the locking valve 952 could be closed,however this would lock the tensioner 910 in position.

Reference is made to FIG. 30, which shows the controller 34. Asdescribed above the controller receives input 960 that may include anyone or more of the following:

Engine ECU Parameters

Time information, which provides daily driver information such as timeof vehicle use, days on/days off and the like;Date information, which provides seasonal time of year approximations,and which may be available from SAT radio/GM OnStar™/Ford Sync™/ECU withbattery backup;Engine information, including RPM (based on crankshaft pulleyspeed)/engine on/engine start successfulTransmission information including transmission gear position & shiftstatus which provides rate of acceleration/deceleration information forbelt slip prediction/transmission downshift & upshift information,Cruise Control information: prolonged steady state speed would implythat use of lower belt tension is permissible/no rapid engine RPMtransitions

Vehicle ECU Parameters

Windshield wiper status—Via CAN busWindshield rain sensor—Via CAN busTraction control system wheel slip status (acceleration)—wheel slippageindicates wet or slushy road conditions—predicts belt contamination/beltslip probabilityABS system wheel slip status (braking)—wheel slippage indicates wet orslushy road conditions—predicts belt contamination/belt slip dangerprobabilityKey fob Sensor in a simple embodiment it can be used to sense theapproach of any driver and can adjust belt tension prior to initial coldengine start. In a more advanced embodiment it can sense approach ofdriver 1/driver 2—and can predicts driver driving style

Ignition Status:

Ignition Status: For a hybrid vehicle stop/start applications—if brakesare applied and if wheel speed=0 and engine RPM=0 would indicate toincrease belt tensionWheel Speed—Hybrid stop/start applications—if brakes are applied AND ifwheel speed=0 AND if engine RPM=0 this is an indication to increase belttensionBrakes—Hybrid stop/start applications—if brakes are applied AND if wheelspeed=0 AND engine RPM=0 then this is an indication to increase belttensionEngine RPM—Hybrid stop/start applications—if brakes are applied AND ifwheel speed=0 AND if engine RPM=0 then this is an indication increasebelt tensionHeadlight Status—If the high beams are on this may indicate fog or someother wet condition in which it would be beneficial to increase belttensionThrottle position sensor, and the Brake position sensor: this includesthe actual positions of the accelerator pedal and brake pedal, and therate of change in the positions of the accelerator pedal and the brakepedal: these may be used to indicate whether the vehicle is coming to astop, is leaving a stopped condition, or is in a panic stop, or is in apanic accelerationDriver selectable settings, such as the driving mode (LUXURY, SPORT,ECO, NORMAL—used to control shift map for the transmission and in somecases the suspension settings). Seat settings, mirror settings and thelike may also be used to indicate to the vehicle which driver is in it,which can be used to indicate whether or not high tension in the belt islikely to be needed.

FEAD Component Information

Battery voltage and battery outgoing currentElectric Fan on/off status—indicates that the alternator may need to bestarted to maintain the battery chargeAlternator regulator status (charge status: on/off)Alternator speed via rotor rotation outputAlternator temperatureAlternator voltageAlternator charge currentHydraulic power steering pressure switch: this indicates power steeringstatus—on/off, if traveling on a highway no turns are anticipated and sothe hydraulic power steering usage is expected to be lowElectric power steering motor status: indicates power steeringstatus—on/off, if traveling on a highway no turns are anticipated and sothe electric power steering usage is expected to be lowAir conditioning compressor clutch state: A/C compressor shaft on/A/Ccompressor shaft offWaterpump SWP clutch state: waterpump impeller on/waterpump impeller offIdler pulley speed (for belt slip calculation where tensioner pulleyspeed sensor is not viable)Tensioner pulley speed (for belt slip calculation where tensioner pulleyspeed is provided)Tensioner arm angle position (measures tensioner arm rotation angleusing the tensioner arm position sensor (e.g. shown at 462)Bumper arm information: This information could include:extended/retracted if using a two position sensor, or could includemultiple positions between extended and retracted positions to providemore precise information regarding the force applied to the tensionerarm by the bumper arm. Optionally a continuous displacement sensor canbe provided to indicate the amount of compression in the second biasingmember more accurately. A load cell sensor could be provided which wouldprovide direct information relating to the amount of force being appliedby the bumper arm to the tensioner arm.Spindle position sensor—measures rotation of spindle—which providesspring tang wind up angle in embodiments where the first end of thebiasing member is moved by the actuator.

Dedicated Sensor Inputs

Temperature sensor for under hood (engine bay) temperature, close toFEAD belt driveHumidity sensor for under hood (engine bay) humidity, close to FEAD beltdriveTemperature sensor—absolute outside ambient outdoor temperatureHumidity sensor—absolute outside ambient out door humidity

Dedicated Sensor and Calculation Procedures and Inputs

Pulley torsional vibration measurement can be as described in PCTpublication WO2006045181 the contents of which are incorporated hereinby reference. Belt elongation and belt stretch measurement can be asdescribed in PCT publication WO2007143830 the contents of which areincorporated herein by reference.Belt flutter/belt twist may be detected as a vibration or as anunderhood noise by acoustic microphones, vibration sensors, or perhaps,by simple “touch” proximity sensors.

Input 960 may also include any other input described herein and mayinclude other inputs also not described herein. The controller 34 usesthese inputs to determine whether or not the change the tension in thetensioner. The controller 34 controls the motor 962 accordingly whichmay be the motor in any of the embodiments described herein.

While the term ‘belt’ has been used and an accessory drive belt has beendescribed in much of the description above, it will be understood thatthe present invention may be applied advantageously to other types ofendless drive member such as a timing belt, a timing chain and any othertype of endless drive member.

While the description contained herein constitutes a plurality ofembodiments of the present invention, it will be appreciated that thepresent invention is susceptible to further modification and changewithout departing from the fair meaning of the accompanying claims.

1-19. (canceled)
 20. A tensioner for a vehicle engine accessory drivesystem having an endless drive member, at least one drive pulleydisposed to drive the endless drive member, and at least one drivenpulley disposed to be driven by the endless drive member and connectedto drive an accessory, the tensioner comprising: a tensioner arm mountedto the engine for movement along a path delimited by a free arm positionand a load stop position; a tensioner pulley rotatably mounted to thetensioner arm, the tensioner pulley engaging the endless drive member; abiasing member arranged to urge the tensioner arm in a first directionalong the path towards the free arm position; and an adjustable loadstop mechanism including a moveable load stop member, a drive mechanismfor moving the load stop member and a controller connected to the drivemechanism; wherein the load stop member arrests movement of thetensioner arm along the path in a second direction, opposite the firstdirection, to thereby define the load stop position; wherein the loadstop member is moveable between a first position correlated to thetensioner free arm position and a second position correlated to atensioner arm position that is maximally displaced from the tensionerfree arm position, and wherein, provided the load stop member is not inthe first position, the tensioner arm is unconstrained by the load stopmember to move in the first direction toward the free arm position;wherein the drive mechanism moves the load stop member to thereby varythe location of the tensioner arm load stop position; and wherein thecontroller directs the drive mechanism to move the load stop membertowards the first position and in the process actively drive thetensioner arm towards the free arm position so as to increase tension onthe endless drive member.
 21. A tensioner as claimed in claim 20,wherein the tensioner arm is pivotally mounted to the engine and thetensioner arm path is arcuate.
 22. A tensioner as claimed in claim 22,wherein the tensioner arm is connected to a housing and the biasingmember acts between the housing and the tensioner arm such that, whenthe tensioner arm is arrested by the load stop member, at least aportion of the reaction load arising from the tension placed on theendless drive member bypasses the biasing member and is borne by theload stop member.
 23. A tensioner as claimed in claim 22, wherein: thetensioner arm is pivotally connected to a first cylinder filled withincompressible fluid; the first cylinder is fluidly connected to asecond cylinder; a first piston is mounted in the first cylinder suchthat as the tensioner arm moves in the second direction the cylinder iscompressed and the incompressible fluid flows into the second cylinder;a second piston is moveably mounted in the second cylinder; the loadstop member is provided by a moveable shaft that projects into thesecond cylinder and is disposed within a travel path of the secondpiston; and wherein the shaft drives the second piston to transfersfluid from the second cylinder into the first cylinder to thereby extendthe first cylinder and move the tensioner arm in the first directiontowards the free arm position.
 24. A tensioner as claimed in claim 23,wherein the second piston is biased into engagement with theincompressible fluid in the second cylinder.
 25. A tensioner as claimedin claim 23, wherein the shaft includes a screw thread meshing with acorresponding nut thread in the second cylinder and the drive mechanismis provided by an electric motor connected via a transmission to rotatethe shaft.
 26. A tensioner as claimed in claim 20, wherein in the engineaccessory drive system a drive pulley and a driven pulley are capable ofreversing roles such that the driven pulley becomes a drive pulley andthe drive pulley becomes a driven pulley.